Data strobe signals (DQS signals) are used for writing and reading of multiple-bit data signals, that is DQ signals when a Central Processing Unit (CPU) performs data input and output to memory. When DQ signals are written to the memory, a memory controller shifts the phase difference between the phase of a DQS signal and the phase of a DQ signal to 90° to each other. In addition, when DQ signals are read from the memory, the memory outputs a DQS signal and a DQ signal in phase. And then the memory controller shifts the phase difference between the phase of the DQS signal and the phase of the DQ signal to 90° to each other to read the DQ signal.
In the adjustments as described above, the phases of DQS signals are fixed and strobe points for writing or reading DQ signals are set at the leading edges of the DQS signals. A plurality of bits of DQ signals are arranged into a group and writing and reading of the plurality of bits of the DQ signals are performed by one DQS signal.
Since each bit of the DQ signals is transmitted via a different transmission line, a certain phase difference between each DQ signal occurs. Therefore, the phase of each DQ signal is adjusted to be in phase based on the strobe point of DQS signal.
In addition, it is conventional to use an eye pattern to adjust the phases of the DQS signals and DQ signals (See patent document 1). Firstly, the phase at which the width of the reference voltage becomes the maximum and the voltage at which the width of the phase for acquiring DQ signal data becomes the maximum are determined in the direction of the reference voltage and the direction of the phase of DQ signal in the eye pattern. And then the strobe point between the DQ signal and the DQS signal are optimized using the determined phase and voltage.
The following patent document describes conventional techniques related to the techniques described herein.